Electric current flows not only in metals, but in liquids and gases. True, the mechanism of electric current flow in these cases is different. In gases, it all starts with an electric discharge. By its nature, it can be of several types, one of them is the so-called glow discharge.
To understand what it is, you can read the description of the experiment conducted by scientists to demonstrate such a phenomenon. To conduct it, use a glass tube of a certain length, which has two electrodes at the ends. They connect a direct current source. Two options for further experiment are possible here: either they begin to gradually increase the voltage to several thousand volts, or they begin to pump air out of the tube until the pressure inside decreases to several mm. Hg. pillar.
When the pressure is reduced to a certain value, a luminous cord flashes from the electrode to the electrode in the tube. This is a glow discharge. Its appearance is promoted by reduced pressure, and it is supported by the secondary emission of electrons from the cathode. The fact is that under ordinary conditions the gas does not conduct electric current, but under special conditions, such as those described, an electric current flows between the electrodes. In this case, positive ions bombard the cathode and knock out electrons from there.
The current flow is due to the formation of such free charge carriers, but the mechanism of their appearance is different. The following types of gas discharges are now known - spark, corona, arc, and smoldering. The reasons why the current begins to flow are also different. When we pump out air from a glass tube, we will finally receive a glow discharge, and when we increase the voltage at the terminals of the electrodes - a spark.
In order not to return to the classification anymore, we note that there are independent and non-independent categories. Types of independent discharges have already been listed, and non-independent discharges occur during any additional external influences.
All types of discharges are interesting and have extremely curious properties, but for now let us dwell on one of them. Let's see what a glow discharge is. If you study its external manifestation, you can establish two areas - non-luminous and luminous. Non-luminous is called the dark cathode space, and luminous is called the positive column, and it occupies almost the entire volume of the tube.
The color of the glow depends on the gas in the medium of which the discharge occurs. Such luminous tubes are used as lamps, the so-called fluorescent lamps. Yes, and advertising lights are also performed using similar tubes. And the process of decoration and lighting design is almost impossible without such products.
However, these are far from all possible applications of a glow discharge. There are industries such as laser technology and plasma chemistry. In addition, due to the use of a glow discharge, the surface of the tool is strengthened to increase its wear resistance, hardness, and cavitation resistance.
Among other possible applications of the described effect, it can be noted its use in special devices based on the glow discharge effect. They can be used to regulate current and voltage, in devices for protection and amplification of devices, oscillation generators. However, electrical discharge can also be an undesirable phenomenon. So, a corona electric discharge with a power line causes energy losses, but this does not apply to the glow discharge, which we are now interested in.
An examination of the electric current in gases made it possible to establish the mechanism of its occurrence, including understanding what a glow discharge is. Variants of its use in industry and technology are described.